Electromagnetic energy sensing may include electromagnetic energy to frequency conversion. This type of electromagnetic energy sensing may be used for light sensing. Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum; light includes ultraviolet light, visible light and infrared light.
A light-to-frequency circuit arrangement, which may also be called light-to-frequency engine, used in a light sensor may have two main components. There is an analog circuit comprising a photo diode and an integrating feedback loop that converts light into a series of pulses. This set of pulses is counted over a fixed period of time by a digital circuit. The number of pulses generated within the fixed period indicates the light intensity. Light-to-frequency converters may be used in applications such as ambient light measurement, light absorption/reflection in products such as white goods, photographic equipment, colorimetry, chemical analyzers and display contrast controls.
Improving the effective resolution of light-to-frequency converters for low light levels for the above-mentioned architecture may be achieved by increasing analog gain and/or increasing the diode area. These approaches may also be used for other architectures. Increasing the low light sensitivity may be achieved by increasing the analog front end gain. This has the side effect of saturation at a lower light level.
It is an aim of the invention to improve the effective resolution of a light-to-frequency converter for low light levels in an alternative way. This is especially important in spectroscopy applications that use a relatively low intensity narrow band source. In these applications, a small spectral response is expected in a different narrow band.